An arrangement as defined above is described in the specification of U.S. Pat. No. 3,907,085 and the corresponding French published patent application No. FR 2 216 856A. That arrangement enables the forces exerted during a declutching operation on the reaction plate of the clutch and on the crankshaft bearings of the vehicle to be minimised. Such an arrangement is applicable to a removable unit comprising at least two cylinders and two pistons, together with a stirrup-shaped casing which may be fitted by simple engagement on a sleeve.
In some cases it may be desirable to use an arrangement having only one piston and one cylinder, arranged concentrically with respect to the shaft which is driven by the clutch when the latter is engaged. In order to satisfy this requirement, an arrangement such as that described in the specification of United Kingdom published patent application No. GB 2 147 668A may be employed. As disclosed in that specification, the cylinder is coupled in rotation with the cover plate of the clutch, with rotary seals being provided between the cylinder and the fluid supply means, the latter being the means for supplying hydraulic fluid for the actuator so as to fill the control chamber defined by the cylinder and piston of the actuator.
However, such an arrangement is complicated and gives rise to sealing problems which can be detrimental to the useful life of the actuator.